1. Field of the Invention
This invention relates to a cutter having a plurality of indexable cutter inserts releasably attached to a peripheral surface of a cutter body adjacent to a forward end thereof.
2. Prior Art
The type of cutters with which the present invention is concerned include a face milling cutter, a boring cutter, a side milling cutter and the like. For simplicity of illustration, however, the invention will be hereinafter described with reference to the face milling cutter. Inserts for use in such a cutter has a quadrilateral shape such as a square, a rectangle, a parallelogram, a rhombus and the like.
Generally, conventional cutters under consideration have been designed to use a plurality of inserts of identical size and shape attached to a cutter body. FIGS. 1 and 2 show one such conventional face milling cutter 100 which comprises a body 101 including a disc-shaped base portion 102 and a boss 103 extending coaxially from the base portion 102 at its rearward end face 104, the boss 103 being adapted to be fixedly secured to a spindle of a milling machine. The base portion 102 of the cutter body 101 has a plurality of recesses 105 formed in its circumferential surface 106 in circumferentially spaced relation to each other and disposed adjacent to its forward end face 107. A plurality of indexable square inserts 108 are received in the respective recesses 105 and clamped thereto by clamp members 111. As shown in FIG. 1, each of the recesses 105 includes a first bearing surface 109 sloping radially inwardly toward the forward end face 107, and a second bearing surface 110 sloping radially outwardly toward the forward end face 107, the first and second bearing surfaces 109 and 110 being disposed right-angularly.
The square insert 108 has four main cutting edges 112 defined by four side faces 116 and a front face 113, and four auxiliary cutting edges 114 at its four corners. For attaching or setting the square insert 108 to the cutter body 101, the insert 108 is received in the recess 105 in such a manner that the two adjacent side faces 116 of the insert remote from the indexed auxiliary cutting edge 114 are held in contact with the first and second bearing surfaces 109 and 110, respectively. Then, the insert is held in position by the clamp member 111 received in the recess 105. The indexed auxiliary cutting edge 114 disposed slightly beyond the forward end face 107 serves as an end cutting edge while the indexed main cutting edge 112 facing away from the first bearing surface 109 serves as a peripheral cutting edge. It is important that the indexed auxiliary cutting edges 114 of all the inserts 108 attached to the cutter body 101 should be located substantially in a common plane perpendicular to an axis X of rotation of the cutter body 101 to form a satisfactory finish surface on a metal workpiece processed by the face milling cutter. Since the two adjacent side faces 116 of the insert 108 supported by the first and second bearing surfaces 109 and 110 are disposed remote from the indexed auxiliary cutting edge 114, the position of the indexed auxiliary cutting edge is liable to be inaccurate due to the manufacturing tolerance of the insert. Thus, the deviation of the auxiliary cutting edge of each insert from its preselected indexing position can not be kept to a minimum.
A conventional face milling cutter 100a shown in FIG. 3 differs from the face milling cutter 100 of FIG. 1 only in that a plurality of recesses 105a formed in a circumferential surface 106 of a cutter body 101 are designed to receive rectangular inserts 108a of identical size. With this conventional face milling cutter 100a, an indexed auxiliary cutting edge 114a is also liable to be displaced out of its proper indexing position when the insert 108a is clamped to the cutter body 101 since it is disposed remote from a pair of bearing surfaces 109a and 110a of the recess 105a against which adjacent longer and shorter side faces 116a and 116b are held respectively.
The square insert 108 (FIG. 4) for use in the conventional milling cutter 100 of FIG. 1 is manufactured using a jig or fixture 117 having a pair of right-angularly disposed supporting surfaces 118 and 119, as shown in FIG. 5. Two adjacent side faces 116 of a square insert blank 108' are held in contact with the pair of supporting surfaces 118 and 119, respectively. In this condition, the corner of the square insert blank 108', disposed in diagonal relation to the corner, at which the two adjacent side faces 116 held against the supporting surfaces 118 and 119 intersect each other, is located or indexed in a machining position. This indexed corner of the insert blank 108' is machined to provide the auxiliary cutting edge 114. A pin 122 of a circular cross-section is used to determine the position of the auxiliary cutting edge 114 to be formed. As shown in FIG. 5, the circumferential surface of the pin 122 serves as a nominal inscribed circle 123 to which the two supporting surfaces 118 and 119 of the jig 117 and hence the two adjacent side faces 116 of the insert blank 108' held against them are tangential. Regardless of dimentional variations .alpha. and .beta. of the insert blank with respect to the nominal inscribed circle 123, the position of the auxiliary cutting edge 114 is determined in such a manner that it is spaced a predetermined distance A from the nominal inscribed circle 123. As a result, the length of the machined auxiliary cutting edge 114 is affected by both of the dimensional variations .alpha. and .beta.. Therefore, the resultant auxiliary cutting edge 114 is susceptible to a relatively large variation in length.
The rectangular insert 108a (FIG. 6) for use in the conventional milling cutter 100a of FIG. 3 are manufactured in a manner similar to that described above for the square insert 108 in FIG. 5. More specifically, as shown in FIG. 7, two adjacent longer and shorter side faces 116a and 116b of a rectangular insert blank 108a' are held in contact with a pair of supporting surfaces 118a and 119a of a jig 117a, respectively. The corner of the insert blank 108a' remote from the supporting surfaces 118a and 119a of the jig 117a is machined to provide the auxiliary cutting edge 114a as described above for the square insert 108. The pin 122 is also used to determine the position of the auxiliary cutting edge 114a to be machined, the circumferential surface of the pin 122 serving as a nominal inscribed circle 123. The position of the auxiliary cutting edge 114a is determined in such a manner that it is spaced a predetermined distance C from the nominal inscribed circle 123. The distance C is determined by a distance B between the inscribed circle 123 and the shorter side face 116b of the insert blank 108a' remote from the supporting surface 119a of the jig 117a. Thus, the positioning of the auxiliary cutting edge 114a is affected by both a dimensional variation .alpha..sub.1 of the insert blank 108a' relative to the nominal inscribed circle 123 and a dimensional variation of the longer side face 116a of the insert blank 108a'. As a result, the resultant auxiliary cutting edge 114a of the rectangular insert 108a is also susceptible to a relatively large variation.
Another conventional face milling cutter 100b shown in FIG. 8 differs from the conventional face milling cutters 100 and 100a of FIGS. 1 and 3 in that each recess 105b is not provided with a bearing surface corresponding to the second bearing surfaces 110 and 110a of the cutters 100 and 100a, so that a bearing surface 109b corresponding to the first bearing surfaces 109 and 109a extends to the circumferential surface 106 of the cutter body 101. This conventional face milling cutter 100b can employ inserts 108a of a rectangular shape as well as inserts 108 of a square shape. For attaching the square insert 108 to the cutter body 101, the forward end of the cutter body is brought into engagement with an upper face of an insert-setting member 126 having a positioning surface 127 disposed in a plane perpendicular to the axis X of rotation of the cutter body 101. The positioning or setting of the square insert 108 is effected in such a manner that one side face 116 of the insert 108 facing away from the indexed main cutting edge 112 is held against the bearing surface 109b of the recess 105b and that the auxiliary cutting edge 114 is held against the positioning surface 127 of the insert-setting member 126. Then, the square insert 108 is fixed to the cutter body 101 by a clamp member (not shown). Inserts 108a of a rectangular shape can be attached to the cutter body 101 in the same manner. With this positioning method, the auxiliary cutting edge 114, 114a can be positioned in its proper indexed position regardless of dimensional variations of the insert. This conventional face milling cutter 100b has been found disadvantageous, however, in that the indexed auxiliary cutting edge 114, 114a is susceptible to damage since it is directly brought into engagement with the insert-setting member 126 during the attachment of the insert to the cutter body 101. Another disadvantage is that it is quite difficult to set the insert on the cutter body 101 attached to the spindle of the face-milling machine since the setting of the insert requires the insert-setting member 126. A further disadvantage is that the insert can not be so easily attached to the cutter body 101 since the insert-setting member 126 is required.